1. Field of the Invention
The present invention relates to a plasma processing apparatus for use in manufacture of semiconductor devices and, more particularly, to a magnetron plasma etching apparatus.
2. Description of the Related Art
Conventionally, a dry etching apparatus, a thin-film forming apparatus, and the like for use in manufacture of semiconductor elements are known as a magnetron plasma processing apparatus. In this apparatus, plasma is generated in a process chamber of the apparatus to perform a desired operation, such as etching and thin-film formation, by the action of ions, radicals, electrons, etc. contained in the plasma.
The magnetron plasma processing apparatus will now be described, taking a magnetron plasma etching apparatus shown in FIG. 1 by way of example.
As shown in FIG. 1, a process chamber 40 is so formed that it can be evacuated and can receive an etching gas. The process chamber 40 includes a plate-like mounting electrode 42 on which a wafer 40 as an object to be processed is mounted, and a plate-like upper electrode 46 arranged in parallel to the mounting electrode 42. Both these electrodes 42 and 46 are formed of conductive material. For example, the upper electrode 46 is grounded, and the mounting electrode 42 is connected to an RF power supply 44 for generating RF power of, e.g., 380 KHz or 13.56 MHz. In this structure, plasma can be generated over the wafer 10 between the electrodes 42 and 46 by a cathode coupling method. Electrons, neutrons, or the like included in the plasma react on or physically act on silicon which forms the wafer 10, thereby etching the wafer 10.
In the magnetron plasma etching apparatus shown in FIG. 1, a magnetic field having a component parallel to the electrodes 42 and 46 is generated between them, as indicated by broken lines, by rotating two permanent magnets 38 supported by a yoke 38b using a rotating shaft 38a. This is because an electric field generated between the electrodes 42 and 46, and the component of the magnetic field perpendicular to the electric field act on the Fleming's rule to cause the cycloid movement of electrons in directions perpendicular to the electric field and the component of the magnetic field to increase the frequency of a collision between the electrons and gas components. Consequently, the amount of plasma generation can be increased, and the etching speed can be increased.
It is required that the etching speed be kept constant on the entire surface of the silicon wafer 10. However, if the conventional plasma etching apparatus is used, wafer etching cannot be uniformed for the following reasons.
(1) The magnetic field generated by the permanent magnets 38 is virtually parallel to the vicinity of the central part of the surface of the wafer 10, and the component of the magnetic field, which is perpendicular to the electric field, is large. In contrast, since the magnetic field generated near the periphery of the wafer 10 is not parallel to the surface of the wafer 10, the perpendicular component of the magnetic field is small. Therefore, the cycloid movement of electrons is hard to occur.
(2) Since the electrons are moved in a direction perpendicular to the magnetic field by the cycloid movement, the density of the electrons is very increased on part of the periphery of the wafer 10, which damages the wafer 10. The ions in the plasma collide with the surface of the wafer 10 by the action of an ion sheath formed between the electrodes 42 and 46. Some of the ions colliding with the surface of the wafer 10, are implanted into the wafer and damage it. When the density of the electrons in the plasma is high, the ions implanted into the wafer 10 are increased in number, with the result that the wafer is greatly damaged. Since the magnetic field is rotated in the magnetron plasma etching apparatus, it is all the periphery of the wafer 10 that is damaged by the ions.
(3) The ion density of etching gas (e.g., Cl) is increased in a region above near the periphery of the wafer 10 more than in a region above near the central part thereof. One reason for this is that the flow (exhaust) of gas generated by etching reaction is slow above near the central part of the wafer 10 and fast above near the periphery thereof.
The above problems are not peculiar to the magnetron plasma etching apparatus but common to a magnetron plasma sputtering apparatus, a plasma CVD apparatus, and the like.